Railway track circuit



Dec. 31, 1935.

F. B. HITCHCOCK RAILWAY TRACK CIRCUIT Filed July 51, 1934 3 Sheets-Sheet 1 Dec. 31, 1935. o 2,026,497

RAILWAY TRACK CIRCUIT I Filed July 51, 1954 5 Sheets-Sheet 2 .vl-m I ail Dean 31', 1935. F. B. HITCHCOCK RAILWAY TRACK CIRCUIT 5 Sheets-Sheet 3 Filed July 31, 1934 Patented Dec. 31, 1935 UNITED STATES PATENT OFFICE RAILWAY TRACK CIRCUIT Application July 31, 1934, Serial No. 737,785

22 Claims.

This invention relates in general to railway signalling track circuits, and pertains more particularly to means for maintaining a substantially constant energization of a track relay associated with a track circuit regardless of changes in leakage current due to variations in ballast conditions between the track rails.

The invention specifically relates to track circuit current regulation or track relay sensitivity regulation automatically effected by a suitable regulator which is locked against operation or change when a train enters the particular track section with which the regulator is associated,

I and is an improvement over the invention disclosed in the prior application of Oscar S. Field Ser. No. 722,934 filed April 28, 1934. I

A normally energized track circuit includes a relay which is maintained energized when the track section is unoccupied, due to current flowing from the track battery through the track rails in series. It is desirable to adjust the normal energizing current in the track relay to a comparatively low value in order to permit the maximum shunt value applied by a train entering the track section to divert sufficient current from the track relay to reduce the energizing current to a degree which will effect the release of the track relay.

The ballast used along a track section permits a certain amount of leakage current to flow between the rails which effects the track circuit current in the same manner as a train shunt. This leakage current, however, is not of a constant value but varies at a relatively slow rate 35 in accordance with the amount of moisture present in the ballast, and consequently the relay current must at times be stepped up and stepped down to compensate for these variations in the ballast condition in order to maintain a substantially constant current value in the track relay to permit reliable operation. On the other hand, the change in the track circuit current varies at a relatively rapid rate upon the entrance and exit of a train.

In view of the above and other considerations, the present invention proposes to provide means automatically operable to maintain a substantial- 1y constant current in the track relay regardless of relatively slow changes in values of leakage curren due to variations in ballast conditions, but to permit a relatively rapid change in current in the track relay in response to the entrance of a train into the associated track section to be effective to cause the release of the track relay before the automatic regulator can become effective to any substantial degree.

In other words, it is proposed to provide a means which automatically distinguishes betweenthe changes in current resulting from different causes in a manner to maintain a sub-- difierent current changes by an automatic lock 1 ing means which operates to prevent a change in the condition of the regulator during the time the associated track section is occupied by a train.

Other objects, purposes and characteristic features of the invention will be brought to light as the description thereof progresses and reference will be made in the description to the accompanying drawings which diagrammatically disclose the invention in a manner to make it easily understood, with no attempt being made to show the particular construction that would preferably be employed in practice and in which:-

Fig. 1 shows in a diagrammatic and conventional manner one form of the present invention as applied to a conventional track circuit.

Fig. 2 shows in a diagrammatic and conventional manner a modified form of the present invention as applied to a conventional track circuit.

Fig. 3 shows in a diagrammatic and conventional manner another modified form of the present invention as applied to a conventional track circuit. I Y

Apparatus-Referring to Figs. 1, 2 and 3, a section of railway track is shown having rails l which are divided from the adjacent track sections by insulated joints 2. In each of these figures, a suitable source of current ET is provided at the right hand end of the track section, which is shown connected to the track rails through a regulating resistor RS.

In this description, it will be assumed that traffic is directed from left to right as indicated by the arrow shown above the track rails of each figure. It will likewise be assumed that signals, such as semaphore signal SG associated with the left hand end of each track section, are used to control'trafiic over the associated track sections and that these signals are governed over the usual control circuits, which are not shown in detail,

but which are indicated by a dotted line as including contact 3 of the track relay in each figure, so that when the sections l are occupied such signals SG are put to stop.

Referring to Fig. 1, a track relay T is shown connected across the left hand end of the track section. In series with relay Tare two regulator relays L and H. Relay L provides the low regulation while relay H provides the high regulation, that is, when relay L is deenergized due to a reduction in current flow through the track relay, it drops its contact and causes an increase in current flow through the track relay to compensate for the reduction due to a change in ballast condition. Relay H acts in the opposite manner, that is, when the track ballast dries out to a predetermined extent, this relay picks up to increase the resistance included in the track relay circuit to compensate for the increase in current flow due to the track ballast drying out.

This increase and decrease in resistance in the track circuit, to thus compensate for variations in ballast conditions, is effected by rheostat PN which is driven by motor M through reduction gear RG. Cam device CM is for the purpose of operating contacts at each extreme position of the rheostat so that the motor circuit is disconnected to prevent driving the rheostat beyond its extreme positions.

Referring to Fig. 2, track relay T is shown connected across the left hand end of the track section in series with resistors IR, 2R, 3R and AR, which resistors may be excluded from the circuit of the track relay by the operation of stepping relays !S, 28, 3S and 48 to maintain a substantially uniform current flow through relay T during variations in ballast conditions.

Relay CVM is a contact making voltmeter hav-- ing a contact 8 which occupies a position out of contact with its right or its left hand contacts as long as the potential across the track relay is within predetermined limits so that relay T will be in its most sensitive condition. Contact 8 is operated to the right and left under various conditions of track ballast to regulate the current through the track relay as will be specifically pointed out. Relay H repeats contact 8 in its right hand position to provide the proper control of the stick circuits of the stepping relays. Since the operation of this circuit requires that potential be connected to conductor 24 for the proper operation of the stepping relays, when the contact making voltmeter is in any except its high position, it will be observed that the connection of relay I-I accomplishes this result.

Referring to Fig. 3, motor M is shown coupled to rheostat PN through reduction gear RG in a similar manner to the disclosure of Fig. 1. In Fig. 3 the cam device and its contacts have been omitted but it will be understood that this device can be provided if desired in the circuit of Fig. 3 to prevent overrun of the rheostat in either of its extreme positions.

The modification in Fig. 3 shows a double wound track relay T operating in conjunction with a primary relay P and a secondary relay S. Resistors RES and RES are provided to compensate for the removal of the lower windings of relays T and P respectively under certain conditions as will be specifically pointed out. Relay I-I corresponds to the high relay of Fig. 1- and operates to control the regulating device when the currentthrough the track relay is increased beyond a predetermined value due to the ballast drying out.

Operation Referring to Fig. 1 and to the positions of rheostat PN and relays T, L and H, it will be assumed that the track section is unoccupied and that there is a slight leakage between the track rails which has caused the rheostat to remove a small amount of its resistance.

Relays T, L and H are normally energized over a circuit extending from the terminal of battery BT, resistor RS, upper track rail, windings of relays H, L and T in series, rheostat PN, and lower track rail to the terminal of battery ET. The current flowing over this circuit under this condition is of such a value that relays T and L are picked up but since relay H is marginal it is not picked up.

Assuming that a train now enters the illustrated track section, the sudden and comparatively low resistance shunt applied to the track rails causes relays T and L to be released. It is assumed that the drop away time of both of these relays is approximately the same but in the event that relay L drops slightly sooner than relay T, the reduction gear between the motor and rheostat PN is sufiicient to prevent the motor operating far enough to appreciably reduce the resistance of rheostat PN which is in the circuit.

When the train leaves the illustrated track section, the sudden increase in current will cause relays T and L to be picked up and because of the reduction gear between the motor and the rheostat, the setting of the rheostat will not be appreciably changed if relay T closes its front contact before relay L opens its back contact.

It will now be assumed that the leakage current between the rails I gradually increases due to increased moisture in thetrack ballast, which shunts some of the current from the windings of the relays. When the current in the windings of the relays reaches a predetermined, value, re- 40 lay L is dropped. This predetermined value at which relay L drops is above the working current or pick up value of the relay T, so that such dropping of the relay L does not affect the relay T. A circuit is now closed for operating motor M in a counter clock-wise direction, which circuit extends from front contact H of relay T, back contact !2 of relay L, back contact l3 of relay H, cam contact M,

right hand field winding l5 of the motor and the armature of the motor, to The operation of the motor in a counter clock-wise direction operates rheostat PN in the same direction to reduce the resistance in series with the relays. When the rheostat reaches a point where the current fiow through these relays is brought to a predetermined value, which corresponds to the pick up value of relay L, this relay will be picked up to stop the operation of the motor.

The converse operation of the regulator will be produced by a reduction in the ballast leakage which will increase the voltage across the terminals of relays T, L and H. This gradually increased voltage across relay H finally reaches the pick up value of relay H and when this relay picks up its contacts a circuit is closed for operating the motorin a clock-wise direction which extends from front contact H of relay T, front contact l2 of relay L, front contact [6 of relay H, cam contact l1, field winding l8 and 70 the motor armature, to

When rheostat PN operates sufficiently far in a clock-wise direction to reduce the potential across the windings of the relays to the drop away value of relay H, the above described circuit is opened at front contact I6 which stops the operation of the rheostat. During this operation relays T and L have remained picked up so that the circuit through back contact I3 of relay H is ineffective when relay H is released.

It is contemplated that the characteristics of rheostat PN and relays T, L and H are so chosen that a reduced potential applied to the terminals of relay L has such an effect on the regulator that the potential applied to the terminals of relay T is automatically maintained substantially constant, irrespective of the drop in potential across these relays due. to the shunting effect of the track leakage. It is of course obvious that the potential across relay T cannot be maintained absolutely constant by such an arrangement, but it will be maintained within such narrow limits that the relay is always at its most sensitive shunting condition.

Referring to Fig. 2 it will be assumed that there is a slight leakage across the rails of the track section which has brought about the picking up of relays IS and 2S to remove their associated resistances IR and 2R from the track circuit. When a train enters the illustrated track section a low resistance shunt is applied across the winding of relay T which causes this relay to drop its contacts. The reduced potential drop across the relay T causes contact 8 of CVM to move to the left. However, the dropping of the front contact 2| locks the stepping relays against further operation because the circuit which controls relay 38 (for example, by Way of front contact 2I which is closed at contact 8 of the contact making voltmeter CVM in its left hand position) is opened by contact 2| before relay SS has time to pick up. When the train leaves the track section, relay T will be picked up and if contact 2| is closed before contact 8 opens, relay 38 will not be picked up because it, as well as all of the stepping relays, are of the slow pick up and slow drop away type.

Relay T is maintained in its sensitive shunting condition in this modification by the operation of the stepping relays in response to the contact making voltmeter CVM. For example, if the leakage between the track rails increases, the voltmeter registers the reduction in potential across the relay T due to this leakage by operating contact 8 to the left. When this potential is reduced to a predetermined value where contact 8 is closed in its left hand position, a circuit is closed for picking up relay 38. This circuit extends from contact 8 in its left hand dotted position, front contact 2| of relay T front contact 22 of relay 2S, and lower winding of relay 38, to 7 It is noted that this value at which contact 8 closes is above the pick up value of the relay T so that it remains in an operated position under such circumstances.

The operation of relay 38 cuts out a section of the resistance in the track relay circuit by short-circuitingresistance 3R at front contact 23. Relay 3S closes a stick circuit for itself extending from back contact 25 of relay H back contact 2%; of relay 48, front contact 21 and upper winding of relay 38, to The stick circuit for relay 23 is now transferred from back contact 28 to at front contact 28 of relay 33. This stick circuit extends through front contact 29 and upperwinding of relay 28, to Relay IS is maintained energized by a stick circuit extending from front contact 30 of relay 28, front contact 3" and upper Winding of relay IS, to

The picking up of front contact 32 of relay 3S closes the pick up circuit of relay 48 but before relay 43 has time to respond, its pick up circuit 5 is opened at contact 8 because this contact moves to the right due to the increase in potential applied to the winding of the voltmeter when resistor 3R is short circuited. If the track ballast shunt continues to increase, contact 8 of the volt- 10 meter will gradually swing to the left again, and will close its left hand contact 8 in response to the potential across relay T again reaching the above mentioned predetermined value. 7

This picks up relay 48 over a circuit extending 15 from contact 8 in its left hand dotted position, front contact 2I of relay T front contact 32 of relay 3S and lower winding of relay 45, to Relay 4S closes a stick circuit for itself extending from back contact 25 of relay H 20 front contact 33 and upper winding of relay 4S, to Relay 48 connects to the stick circuit of relay 38 at front contact 26. Relay 48 also short-circuits resistance 4R at front contact 34 which increases the current flow through the 25 track relay and in response to such corresponding increase in potential across the relay'T due to this increased current flow, the voltmeter operates its contact 8 away from its left hand position. 3O

' It will be understood that additional relays may be provided and connected in the same manner as the four stepping relays which are illustrated, if additional resistances similar to IR to AB inclusive are required for the length of track circuit with which this regulator is to be used, with thesuccessive sections of these resistances divided in accordance with the regulation curve of the track circuit.

It will now be assumed that the relays are in 40 the positions illustrated in Fig. 2 and that the track ballast dries out to the point where, the contact making voltmeter closes its contact 8 in its right hand dotted position. This closes an obvious circuit for picking up relay H Relay H opens its back contact 25 which deenergizes the stick circuit of relay 28 allowing this relay to drop and by opening its front contact 35 it inserts resistance 2R in the track circuit. This increase in resistance reduces the current flow through the track relay circuit and the resulting decrease in potential drop across the winding of the voltmeter, causes its contact 8 to swing to the left which drops relay H The closure of back contact 25 of relay H energizes the stick conductor 24 which maintains relay IS picked up over a circuit extending from this conductor, back contact 30 of relay 28, front contact 3| and upper Winding of relay IS, to Due to the slow releasing characteristics of the stepping relays, relay IS is not dropped when this transfer is made.

If the track continues to dry out to the point where contact 8 is again closed, relay 1-1 will be picked up to again deenergize stick conductor 24 which will drop relay IS to insert resistanceIR in the track relay circuit by opening its front contact 36. The voltmeter contact 8 will then swing to the left to drop relay H which energizes stick conductor 24 but since relay IS is the first of the series the energization of this conductor is ineffective.

From' the above it will be obvious that the stepping relays are picked up in sequence in response to the slow leakage shunt conditions applied to the track circuit, with each stepping relay reducing the resistance in series with the track relay to compensate for the drop in potential due to the leakage. Conversely when the track section dries out, the stepping relays are dropped in sequence to insert resistance in the track relay circuit to compensate for the increase in po tential across-its winding due to the reduction in ballast shunt. Thus, the potential across the terminals of relay T is maintained within predetermined limits, which renders this relay capable of responding to the occupancy and the unoccupancy of the track section in an effective manner.

It will be understood that relays L and H of Fig. 1 may be used in place of the contact making voltmeter of Fig. 2 to control the operation of the stepping relays if desired. It will also be understood that the contact making voltmeter of Fig. 2 may be used in place of relays L and H of Fig. 1 to control the motor driven rheostat.

Referring to Fig. 3, primary relay P and secondary relay S operate in conjunction to maintain the current through the upper winding of track relay T within very narrow limits in response to increased leakage between the track rails due to poor ballast conditions. Relay H functions to maintain the operating current through the upper winding of relay T within very narrow limits as the track ballast dries out.

Relay P is provided with a comparatively small number of contacts and a generally lighter armature than relay S, which provides a mechanical structure whereby the operation of the armature is efiected with maximum sensitivity, efliciency and speed. Secondary relay S is of a more powerful construction since it is controlled over a circuit which is entirely local and over which the current flow does not vary to any appreciable extent.

Primary relay P is provided with a tapped winding which is connected in part or in whole across the track circuit in series with relays T and H as well as rheostat PN in accordance with the energized or deenergized position of the contacts of relay S. Secondary relay S is arranged by any well known means to have a normal pick up time which is considerably less than its drop away time, such a means for effecting such operation may be the provision of short circuited windings, copper slugs or the like.

When the track section is unoccupied both relays P and S are maintained energized as shown. Relay P is energized over a circuit extending from the terminal of battery BT, resistor RS. upper track rail, upper winding of relay T windings 54 and 55 of relay P in series, resistance RES front contact 51 of relay S, front contact 58 of relay S, winding of relay H rheostat PH, and lower track rail to the terminal of battery ET. The current flowing in this circuit is sufficient to maintain relays T and P picked up but insuficient to pick up relay H When the track section becomes occupied by a train sufiicient current is shunted through the wheels and axles to effect the releasing of relays T and P. The dropping of relay T opens the circuit of relay S at front contact 59 and after a short interval of time relay S drops its contacts 51 and 58. Since contact 59 of relay T is open, the closure of back contact 60 of relay P is ineffective to energize the motor which has the effect of locking the rheostat in the position it occupied when the track became occupied.

The dropping of contact 51 of relay S shifts the circuit to exclude resistance RES and to insert winding 56 of relay P in the circuit and since these windings of the relay P are cumulatively wound, the total winding is now efiective to increase the sensitivity of relay P so that it will be more positively picked up when the train shunt is removed. As the winding 55 and resistance RES are equal in resistance, the reduced current in the three windings of relay P remains constant during the shunted condition of the track. Irrespective of the increased number of turns of relay P which are effective, the increased magneto-motive force is insufficient to attract its armature. This is because the shunting efiect produced by the train prevents sufficient magneto-motive force being applied to the armature of relay P to bring this force up to the pick up value of the relay, although such value of magneto-motive force is now above the drop away value.

When the train leaves the track section, how;- ever, relay P has the advantage of the increased number of ampere turns, due to the insertion of its winding 56 in the track circuit, so that it will be positively picked up. The dropping of contact SI of relay T has a similar effect on its own sensitivity by shifting the track circuit from resistance RES to the lower winding of relay T both of which have equal values of resistance. This increases the sensitivity of relay T so that the removal of the train shunt from the track supplies both windings of relay T with sufficient current so that the magneto-motive force produced by this current is considerably above the pick up value of the relay. It will be understood that the resistance values of relay H and the lower winding of relay T are equal.

When contacts 59 and 60 of relays T and P are picked up, relay S is again picked up to place the circuits in their original condition. This removes winding 56 of relay P from the track circuit and also the lower winding of relay T so that these relays are rendered more sensitive to the shunting effect of the train.

Assuming the apparatus in the condition shown in Fig. 3, it will be assumed that a slowly increasing, shunt is applied across the rails of the track due to a wet ballast condition. This increasing shunt causes relay P to drop its contacts 53 and 50 when the drop away value of this relay is reached, which drop away value is above the drop away value of relay T dropping of contact 53 is ineffective at this time. The opening of front contact 60 deenergizes relay S which shifts the circuit to again include winding 56 of relay P to make it more sensitive to pick up.

The closure of back contact 60 of relay P operates the motor in a counter clock-wise direction over a circuit extending from front contact 59 of relay T back contact 60 of relay P, back contact 62 of relay H field winding 63 and armature of the motor, to This reduces the resistance of rheostat PN which is included in the track circuit which has the effect of increasing the current flow through the windings of relay P until the pick up value of this relay is reached. Relay P picks up its contact 60 which stops the motor and again energizes relay S. This places the circuit back in the most sensitive condition for shunting relay P. It will be understood that during this operation the current through'the track circuit does not reach the drop away value of relay T3.

If the ballast shunt continues to increase, relay P will again be dropped to operate the motor for further reducing the resistance of rheostat PN in the track circuit until relay P receives sufiicient current to again pick up and stop the operation of the motor. This continues each time the track becomes sufficiently shunted to drop relay P and it will be observed that the circuit arrangement is such that the current through-the operating (upper) winding of relay T is maintained within very narrow limits.

Assuming now that the track begins to dry out. This has the effect of reducing the shunt across the track rails which allows more and more current to flow through the circuit including the winding of relay H when relay H will pick up its contacts which closes a circuit for operating motor M in a clockwise direction, which circuit extends from front contact.53 of relay P, front contact 64 of relay H field winding 65 and armatureof the motor, to This operation of the motor increases the resistance of rheostat PN in the circuit until the drop away value of relay P is reached. Relay P stops the operation of the motor by opening its front contact 53 and at its front contact 60 it deenergizes relay S.

When relay S opens its front contact 58, relay H is deenergized and the closure of back contact 51 places the windings of relay P in the condition for the most sensitive pick up of this relay. The dropping of relay H closes a circuit for energizing the motor through its counter clock-wise field winding 63, which circuit extends from front contact 59 of relay T back contact 60 of relay P, back contact 62 of relay H field winding 63 and armature of the motor, to The motor will now be operated in its counter clock-wise direction to reduce the resistance of rheostat .PN in the circuit until the pick up value of relay P is reached. The picking up of relay P then stops the motor and places the circuits in normal condition.

This operation continues each time the track ballast dries out to the point where relay H is picked up, that is, relay H picks up, operates the motor in a clock-wise direction until sufiicient resistance of the rheostat has been connected to the circuit to drop relay P, after which the motor is reversed to reduce the resistance of the rheostat until relay P picks up to stop the motor in a position which places the track circuit in its most sensitive or normal operating condition. It will of course be understood that track relay '1' is not efiected by this operation but maintains its contacts picked up until a train shunt is applied.

It is to be understood that the motor driven rheostat of Fig. 3 may be replaced by the stepping relay regulator of Fig. 2 without departing from the scope of the invention.

The above rather specific description of three forms of the present invention is given solely by way of example and is not intended in any manner whatsoever in a limiting sense. It is to be understood that various modifications, adaptations and alterations may be applied to meet the requirements of practice without in any manner" departing from the spirit or scope of the invention except as limited by the appended claims.

What I claim is:- 1. In a track circuit, an insulatedsection of track, a source of current connected across one end of said track, a track relay connected across A point will be reached the other end of said track, a regulator including a variable resistance connected in series'with said track relay, a first relay contact closed in response to a reduced potential across said track relay due to a gradually increasing shunt across said track, a second relay contact closed in response to an increased potential across said'track relay due to a gradually decreasing shunt across said track, means controlled by said contacts for causing said regulator to vary the value of said resistance, and means controlled by said track relay for locking said regulator.

2. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a sensitive and a marginal relay connected in series with said track relay, 2. rheostat connected in series with said relays, means responsive to variations in track ballast conditions for operating said sensitive and marginal relays, and means responsive to the operation of said sensitive and marginal relays for controlling the operation of said rheosat.

3. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a. sensitive and a marginal relay connected in series with said track relay, a rheostat. connected in series with said responsive to the occupancy of said track section for preventing the operation of said rheostat by said relays.

4. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a sensitive and a marginal relay connected in series with said track relay, a rheostat connected in series with said relays, means responsive to an increase in track ballast leakage for operating said sensitive relay, means responsive to a decrease in track ballast leakage for operating said marginal relay, and means responsive to the operation of said relays for operating said rheostat whereby the potential across said track relay is maintained substantially constant irrespective of changes in ballast leakage.

5. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a sensitive and a marginal relay connected in series with said track relay, a rheostat connected in series with said relays, means responsive to an increase in track ballast leakage for operating said sensitive relay,

means responsive to a decrease in track ballast leakage for operating said marginal relay, means responsive to the operation of said relays for operating said rheostat whereby the potential across said track relay is maintained substantially constant irrespective of changes in ballast leakage, and means responsive to the occupancy of said track by a train for operating said track relay whereby said rheostat is locked against operation.

'6.'In a track circuit, an insulated section oi track, a source of current connected across one end of said track, a track relay connected across the-other end of said track, a resistor connected in series with said track relay, a stepping relay bank, means responsive to the operation of said stepping relay bank for varying the value of said resistor which is included in series with said track relay, means responsive to variations in track ballast leakage for operating said stepping relay bank, and means responsive to the occupancy of said section by a train for preventing operation of said stepping relay bank.

7. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay and a contact making voltmeter connected across the other end of said track, a resistor connected in series with said track relay, a stepping relay bank, means responsive to the operation of said stepping relay bank for varying the value of said resistor which is included in series with said track relay, means responsive to shunts provided by a train and ballast leakage for operating said voltmeter, means including said voltmeter and responsive to variations in track ballast leakage for operating said stepping relay bank, and means responsive to a train shunt for preventing operation of said stepping relay bank.

8. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a resistor connected in series with said track relay, a stepping relay bank, means responsive to the operation of said stepping relay bank for varying the value of said resistor which is included in series with said track relay, means responsive to an increase in track ballast leakage for picking up the relays in said bank in sequence, and means responsive to a decrease in track ballast leakage for dropping the relays in said bank in sequence.

9. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a resistor connected in series with said track relay, a stepping relay bank, means responsive to the operation of said stepping relay bank for varying the value of said resistor which is included in series with said track relay, means responsive to an increase in track ballast leakage for picking up the relays in said bank in sequence, means responsive to a decrease in track ballast leakage for dropping the relays in said bank in sequence, and means controlled by said track relay for locking said stepping relay bank in the condition existing when said track section becomes occupied by a train.

10. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a primary relay connected in series with said track relay, a secondary relay, means responsive to the operation of said secondary relay for connecting an additional winding of said primary relay in series with said track circuit, means responsive to the occupancy of said track section for operating said track relay and said primary relay, and means responsive to the operation of said track relay and said primary relay for controlling the operation of said secondary relay.

11. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected'across the other end of said track, a primary relay and a rheostat connected in series with said track relay, a secondary relay, means responsive to the operation of said secondary relay for connecting an'additiona-l winding of said primary relay in series with said track circuit, means responsive to the occupancy of said track section for operating said track relay and said primary relay, means responsive to the operation of said track relay and said primary relay for controlling the operation of said secondary relay, and means responsive to the operation of said primary relay for controlling the operation of said rheostat.

12. In a track circuit, an insulated section of track, a source of current connected across one 10 end of said track, a track relay connected across the other end of said track, a primary relay and a rheostat connected in series with said track relay, a secondary relay, means responsive to the operation of said secondary relay for connecting an additional winding of said primary relay in series with said track circuit, means responsive to the occupancy of said track section for operating said track relay and said primary relay, means responsive to the operation of said track relay and said primary relay for controlling the operation of said secondary relay, means responsive to the operation of said primary relay for controlling the operation of said rheostat, and means controlled by said track relay for preventing the operation of said rheostat.

13. In a track circuit, an insulated section of track, a source of current connected across one end of said track, a track relay connected across the other end of said track, a primary relay and a rheostat connected in series with said track relay, a secondary relay, means responsive to the operation of said secondary relay for connecting an additional winding of said primary relay in series with said track circuit, means responsive to the occupancy of said track section for operating said track relay and said primary relay, means responsive to the operation of said track relay and said secondary relay for connecting an additional winding of said track re- 4 lay in series with said track circuit, means responsive to the operation of said track relay and said primary relay for controlling the operation of said secondaryrelay, and means responsive to the operation of said primary relay for controlling the operation of said rheostat.

1%. In a track circuit, an insulated section of track,- a source of current connected across one end of said track, a track relay connected across the other end of said track, a primary relay and a rheostat connected in series with said track relay, a secondary relay, means responsive to the operation of said secondary relay for connecting an additional winding of said primary relay in series with said track circuit, means responsive: to the occupancy of said track section for operating said track relay and said primary relay, means responsive to the operation of said track relay and said secondary relay for connecting an additional winding of said track relay in series with said track circuit, means responsive to the operation of said track relay and said primary relay for controlling the operation of said secondary relay, means responsive to the operation of said primary relay for controlling the operation of said rheostat, and means for equalizing the resistance value connected to said track circuit under the various operated positions of said relays.

15. In combination, an insulated track section, a track relay and a source of current connected across the rails of said section at opposite ends,

a contact making voltmeter and a series of stick relays, means including said voltmeter and said relays for automatically adjusting the potential across the track rails, means controlled by said voltmeter for operating said relays under one potential condition and for releasing said relays under another potential condition, and locking means for preventing said potential adjustment across the track rails.

16. In combination, a section of railway track, a source of electric potential connected across one end of said section, a track relay connected across the other end of said section, a variable resistor connected in series with said track relay, operating means for relatively slowly increasing and decreasing the resistance value of said resistor when rendered effective, a first contact closed in response to a predetermined increase in potential across said track relay for rendering said operating means efiective to increase the resistance value of said resistor, a secpnd contact closed in response to a predetermined decrease in potential across said track relay for rendering said operating means efiective to decrease the resistance value of said resistor, and a contact on said track relay opened in response to a relatively quick decrease in potential across said track relay greater than said predetermined decrease for rendering said second contact inefiective to control said operating means.

17. In combination; a section of railway track; a source of electric potential connected across one end of said section; a track relay having predetermined pick up and drop away values connected across the other end of said section;

a Variable resistor connected in series with said ,t'rack relay; operating means for increasing and decreasing the resistance of said resistor, when rendered efiective; electro-magnetic means responsive to potential changes across said track relay and having a first contact closed in response to a predetermined increase in potential across said track relay above the pick up value for said track relay, a second contact closed in response to a predetermined decrease in potential across said track relay which decrease value is above the drop away value of said track relay, said electro-magnetic means acting at substantially the same rate of response as said track relay; and means controlled by said first and second contacts for respectively rendering said operating means efiective to increase or decrease the resistance value of said resistor, said means acting only when said track relay is picked up.

18. In combination, a section of railway track, a source of electric potential connected across one end of said section, a track relay having a predetermined operating value and connected across the other end of said section, a marginal relay connected in series with said track relay and having a pick up value a predetermined amount above the operating value of said track relay, a sensitive relay having a drop away value substantially the same as or above the operating value of said track relay but below the pick up value of said marginal relay, a variable resistor connected in series with said relays, means responsive to the picking up of said marginal relay for increasing the resistance of said variable resistor, means responsive to the dropping away of said sensitive relay to decrease the resistance of said variable resistor, and means efiective upon the dropping away of said track relay to prevent the varying of resistance in said variable resistor by said sensitive and marginal relays.

it. In combination, a section of railway track, a source of electric potential connected across I one end of said section, a track relay connected relay is returned to a normal operating value, 10

means responsive to an increase in potential across said track relay for dropping said stepping relays in a reverse sequence to increase the resistance of said variable resistor until the potential across said track relay is returned to a normal operating value, and means elfective uponith'e dropping of said track relay to preventthepiclbn ing up of stepping relays without afiecting any of the stepping relays already picked up.

20. IlFc-ernbinatigma section of railway track; 2Q;

a source of electric pten'tlalconnected-acrossbne end of said section; a track relay having.prede-' termined pick up and drop away values and connected across the other end of said section; a

variable resistor connected in series with said track relay; a stepping relay bank; means responsive to the operation of said stepping relay bank for varying the value of said resistor which is included in series with said track relay; electromagnetic means responsive to potential changes across said track relay and having a first contact closed in response to a predetermined increase in potential across said track relay above the pick up value of said track relay, a second contact closed in response to a predetermined decrease in potential across said track relay which decreased value is above the pick up value of said track relay, said electro-magnetic means acting at substantially the same rate of response as said track relay; means controlled by the closure of said sec- 40 0nd contact for picking said stepping relays up in sequence; means controlled by the closure of said first contact for dropping said relays in a reverse sequence; and a contact on said track relay for rendering said second contact inefiective; where- 5 by an increase or decrease within said predetermined value is compensated, but a decrease below the drop away value of said track relaycausing substantially simultaneous dropping of said track relay and closure of said second contact maintains said track deenergized and prevents compensation.

21. In combination, .a section of railway track, a source of electric potential connected across one end of said section, a track relay connected across the other end of said section, a contact making voltmeter having a moving contact biased to one position and arranged to close a back contact at a predetermined potential across said track relay and arranged to close a front contact at a predetermined higher potential across said track relay both of such potentials being within the operating range of said track relay, a variable resistor connected in series with said track relay, operating means for slowly increasing or decreasing the resistance value of said variable resistor upon the closure of said front and back contacts respectively, and a front contact on said track relay for preventing the control of said operating 76 into said section causes the dropping away of said track relay and prevents a change in the value of said resistor.

22. In combination, a section of railway track; a source of electric potential connected across one end of said section; a track relay having a predetermined operating value and connected across the other end of said section; a variable resistor connected in series with said track relay; operating means for increasing and decreasing the resistance of said resistor, when rendered effective; electro-magnetic means responsive to potential changes across said track relay and having a first contact closed in response to a predetermined increase in potential across said track relay which increased value is above the operating value of said track relay, a second contact closed in response to a predetermined decrease in potential across said track relay which decreased value is above the operating value of said track relay; and means controlled by said first and said second contacts for respectively rendering said operating means effective to increase or decrease the resistance value of said resistor, said means acting only when said track relay is picked up; whereby an increase or decrease in potential within said predetermined values is compensated for but a decrease below said operating value of said track relay causes said track relay to drop away and prevent compensation.

FOREST B. HITCI-ICOCK. 

